Vehicles operating in an autonomous mode (e.g., driverless) can relieve occupants, especially the driver, from some driving-related responsibilities. When operating in an autonomous mode, the vehicle can navigate to various locations using onboard sensors, allowing the vehicle to travel with minimal human interaction or in some cases without any passengers.
Vehicles can operate in an autonomous mode by a planned driving trajectory. A planned driving trajectory is generated by an ADV's planning module relying on “reference lines”. A reference line is a smooth line on a geometric word map. Reference lines are represented by a set of points along a road curve. A typical 200 meter road curve uses 1000 points for a reference line. The computation time for many algorithms, such as reference line projections and driving trajectory decision and planning, are directly related to the number of points or density of a reference line.